The present invention relates generally to the field of refrigeration circuits, and, in particular, to a manner of passively defrosting the drain from an evaporator.
A common refrigeration circuit is a vapor-compression system comprising a compressor, a condenser, an expansion valve, and an evaporator. A refrigerant is circulated through the circuit such that the compressor raises the pressure of the refrigerant vapor so that its saturation temperature is slightly above the temperature of an available cooling medium, such as air or water. The difference in temperature allows transfer of heat from the vapor to the cooling medium so that the vapor can condense in the condenser.
Next, the liquid expands, via the expansion valve, to a pressure such that its saturation temperature is slightly below the temperature of the space (or product) to be cooled. This temperature difference allows transfer of heat from the space to the refrigerant, causing the refrigerant to evaporate in the evaporator. The vapor formed is removed by the compressor such that the low pressure in the evaporator, and thus the refrigeration cycle, is maintained. In absorption refrigeration systems, the compressor is replaced by an absorber and generator, while retaining the condenser, flow control and evaporator.
In refrigerators, an evaporator is located in the freezer compartment and a second evaporator may be located in the cold storage compartment of the refrigerator. These evaporators are typically exposed to air in the space of the freezer and cold storage compartments. As the freezer or cold storage space is cooled, condensation forms and freezes on the exterior of the evaporator, which contains the refrigerant vapor. Periodically, a defrost cycle is initiated to melt the accumulated ice.
A drain pan or tray is usually placed below the evaporator, and has a hole for collected condensation to flow through a drain line for removal. Frost and ice formation at the tray hole and in the drain line is typical, due to the cooling of the space near the evaporator, with the result that the flow of the condensation away from the evaporator is obstructed.
One method of defrosting the drain is the use of an electric device. The use of electric coils or the like results in increased power usage and therefore higher operating costs of the refrigerator. The inclusion of the coils at the drain of the evaporator adds to the manufacturing complexity and cost of the refrigerator. Also, incorporation of the electric device into the refrigerator may reduce the amount of usable freezer or cold storage space.
Another method of defrosting the drain is by the rerouting of a heated portion of the refrigeration circuit so that a heated tube passes close to the drain as disclosed in U.S. Pat. No. 4,420,943. However, this reduces the efficiency of the refrigerator, as heat is lost from the refrigeration circuit to defrost the drain. The loading on the components of the circuit is increased, with a corresponding increase in the operating costs of the refrigerator.
The use of insulation wrapped around the drain line is inefficient for defrosting the drain, and the insulation material is subject to deterioration and loss of performance from the constant freezing conditions near the evaporator.
In view of the foregoing, a need exists for an improved evaporator drain defroster that overcomes the problems mentioned.